1. Field of the Invention
This invention relates to an improved circuit package. More particularly, it relates to an integrated circuit package having an integral heating circuit for use in raising the temperature of the integrated circuit package sufficiently to melt solder for use in removing the integrated circuit package from a system, or making reflow reconnect into a system.
2. State of the Prior Art
The fabrication of integrated circuit components involves the fabrication of an integrated circuit die, often referred to as a chip, that performs the desired electrical or logical function. Chips are of varying sizes, with the main thrust of development to further miniaturize. Miniaturization leads to availability of ever-increasing logic of circuit functions on smaller substrates. Miniaturization increases circuit density and tends to require more leads to be provided for input and output signals and application of power. As leads were made smaller, manual installation and removal techniques became inefficient and in many cases almost impossible to accomplish.
In order to make interconnection to the integrate circuit substrate or chip, it is common to provide a package that will make interconnection with the terminals on the chip and provide means for making electrical interconnection into the system with which the chip will be used. The package characteristically supports the chip, and includes circuit interconnections for making electrical connection to terminals on the chip, and for making electrical interconnection to pins for interconnecting the wiring in a support assembly.
In the fabrication process, it is known to provide advantageous results to utilize step soldering techniques. This involves selecting solders that melt at different temperatures for use in different steps of fabrication. For example, a relatively high melting temperature solder is utilized for soldering the chip to the leads of the integrated circuit package. When a cover is to be soldered over the chip cavity, a medium temperature solder is selected. A relatively low melting temperature solder is selected for making the electrical interconnection of the terminals of the integrated circuit package to the pins that mount to the support chassis. Through utilization of the step solder selection, sufficient heat can be applied to melt the solder, thus allowing removal of the integrated circuit package from connection with the chassis without causing the entire assembly to be unsoldered.
Once the chip and integrated package have been installed in an operating system, it sometimes is necessary to accomplish removal for maintenance and repair purposes. In the prior art, various systems and techniques have been devised for applying sufficient heat to the integrated circuit terminals of package to cause the solder making connection with the chassis pins to melt. One such technique is to provide a heated air jet that is applied directly on the package terminals. The characteristics of air are such that it must be raised to an extremely high temperature in order to provide sufficient thermal transmission to melt the solder. Further, due to the very small size of the integrated circuit packages, it is extremly difficult to accurately direct the air flow on the interconnecting pins. The air flow technique is relatively slow and requires special rework equipment.
Another prior art technique to remove integrated circuit packages is to simply apply a conventional soldering iron to the surface of the package. This allows the heat from the iron to permeate through the package and melt the solder at the chassis pins for either removal or reinsertion of the integrated circuit package. This system has many disadvantages but presently is the most widely used system due to general availability of soldering irons at rework or test facilities. A primary problem is the unknown temperature of the tip of the iron when it is applied to the integrated circuit package. Characteristically, the iron is pre-heated, and a 100 Watt iron can have tip temperature on the order of 420.degree. Centigrade. When preheated to a temperature that will provide adequate heat transfer to the package, it is not uncommon for the soldering iron to be at a temperature more than two times that required to melt the pin solder. This high temperature can lead to the undesired results of cracking the package material, damaging the chip, and raising the entire assembly to a temperature that causes melting of all of the solder types in the package. For rework and reinstallation, the uncontrolled application of heat is difficult to control and can cause the cover to become unsealed from the package or cause the chip to lose good contact to the package. In addition to damage to the integrated circuit or the package, this application of heat can result in damage to heat sinks that might be associated with the circuit.
Tools have been developed which are designed to contact each solder joint, but such tools have been found to interfere with the formation of a new solder joint when a replacement part is installed. These tools also have been found to fail to contact all solder joints equally.